This invention is directed to a slurry metering valve and, in particular, to a valve for metering a relatively small amount of slurry from a larger continuously flowing fluid stream. The invention is also directed to a slurry metering valve which is self-cleaning so as to avoid plugging of the valve and stoppage of metered flow.
When metering a relatively low volume flow of slurry from a feed source to a desired destination for processing, it is necessary to include a circulation loop back to the feed source so that when the metered slurry flow is off-line, the loop stream maintains the slurry fluid and prevents the segregation of the solids from the liquid carrier. Alternative methods have been used to meter a slurry. In one such system, a conventional three-way ball valve containing two outlet ports is used in which the slurry flow from the feed source is alternately sent to one of the outlet ports communicating with either the loop stream or the metered stream. Thus, the ball valve operates as an on and off valve in which slurry flow through the relatively low volume metering line requires that flow through the circulation loop be stopped and vice versa. In applications where transport lines are very small and very low velocities are utilized, the on-off pattern of a typical three-way valve results in gross non-uniform flow as the solids settle and separate from the liquid carrier during flow stoppage both in the circulation loop and in the lower volume metering line. Plugging or substantial non-uniform flow in the lower volume metering line means that the slurry has to be constantly diverted into the circulation loop to maintain the slurry fluid, drastically reducing end use processing rates of the slurry being metered. Alternatively, a slurry metering system has been used which includes the circulation loop to and from the slurry feed wherein the circulation loop is split with a T-connector to divide the slurry flow between the circulation loop and a metering valve which meters the slurry to the desired processing unit. However, the slurry stagnates in the line between the metering valve and the T-connector as the metered flow has a substantially lower volume flow compared to the flow rate of circulation loop- Again, this stagnation leads to solids segregation and plugging, and consequent non-uniform metered flow and reduced processing rates. Accordingly, there is still a need to provide a useful slurry metering valve which can substantially reduce, if not eliminate, the uneven metered flow of a slurry to processing.
Similar to the valve of the present invention which is described hereinafter, valves have been provided to remove from a primary fluid flow a secondary or lower volume flow. For example, U.S. Pat. No. 582,507, issued May 11, 1897, discloses a valve used to remove condensate from a steam line and which includes a passage therethrough for the main flow of gas and a valve stem which passes through the main flow and is seated upon a valve seat which contains a passage from the main flow and directed therefrom. When the valve stem is not seated, condensation in the main gas flow passes through the valve seat and away from the valve and main flow of gas.
U.S. Pat, No. 4,281,935, issued Aug. 4, 1981, discloses a similar valve containing an inlet and outlet for a primary fluid flow, a valve stem which passes through the primary flow and is seated on a valve seat which is located directly across the primary flow path relative to the valve stem and extends into the primary flow. The valve seat includes a passage communicating with the primary flow and with a separate inlet/outlet portion of the valve. The valve is disclosed as being primarily useful for injecting a fluid into the primary flow through the passage contained in the valve seat but, conversely, can be used to remove a small portion of the primary flow through the passage in the valve seat. The valve stem can be rotated relative to the valve seat to clean the same. The valve stem is seated and rotated such as by a hand-wrench as the valve stem and seat are in contact.
Neither of the above patents, however, are concerned with continuously metering a secondary flow from a continuous primary flow. Instead, the patents merely seem to be concerned with an on-off flow of the secondary stream to or from a primary flow stream. Additionally, the patents are not concerned with metering a slurry stream or concerned with the problems attendant therein such as non-uniform flow as the slurry segregates and plugging which may occur upon segregation of the slurry and accumulation of the solids in the valve passages. While U.S. Pat. No. 4,281,935 discloses a cleaning feature, it is necessary that the secondary flow be shut-off from the main flow to clean the valve stem and seat inasmuch as the cleaning action is provided by contacting the valve stem with the valve seat which effectively closes the passage in the valve seat from the primary flow. Thus, the cleaning procedure effectively shuts down the removal of the secondary stream from the primary flow.
Accordingly, it is an object of the present invention to provide an improved metering valve for slurries.
Another object of the present invention is to provide a metering valve which will allow the continuous removal and transport of a relative low volume metered flow of slurry from a primary flow of slurry.
Still another object of the present invention is to provide a slurry metering valve which has self cleaning features so as to maintain a continuous flow of slurry through the valve.
Further still, another object of this invention is to provide a process for continuously metering a flow of slurry from a primary feed source to a processing unit with reduced plugging and without adverse nonuniform flow.